There are a range of existing systems for locating mobile phones. These can be grouped into three categories as follows:
Network based systems. Such systems perform the signal parameter measurements as well as the location calculation in one or more network based servers.
Handset based systems. In these systems, both the measurements and the location calculations are performed in the handset.
Hybrid. In these systems the measurements are performed in one place while the position calculation is performed in another. For instance the handset may make the measurements and report them to a network based entity where the location calculations are performed. In some cases the measurements are pre-processed before sending.
Limitations of Current Systems
When operating a particular location based service, a key determining factor in the success of the service is the cost to the user. In the case of location based services, a large proportion of this cost is due to actually obtaining the location estimate. In many cases, this cost is incurred primarily in obtaining the signal parameter measurements for the location calculation. As an example, in a handset assisted hybrid system, the network based entity has to open a connection to the mobile and request the measurements. The handset in turn must transmit the measurements to the requesting entity. This exchange consumes network resources and as a result incurs a cost. Further the network resources are finite and thus limiting the number of users that can be tracked simultaneously as well as necessitating a compromise with respect to other services that require the network resources. In the following paragraphs we will outline the limitations of current systems compared to the system of this invention. The primary limitations are either excessive cost or inadequate performance.
Network Based Systems
In network based systems, network based equipment measures parameters of signals received from the mobile. The measuring equipment may be existing mobile network base stations or ancillary receivers installed as an overlay to an existing network. In either case there is a fundamental requirement for the mobile to be transmitting in order for signals to be available for measurement. This represents a serious limitation for any location based service where frequent monitoring of a mobile's location is needed but the use of the location for commercial benefit is much less frequent. To illustrate, consider a mobile advertising application. A particular store or chain wishes to know when a registered customer approaches a store. The aim is to transmit a targeted advertisement perhaps accompanied by a time limited discount offer to entice the recipient into the store. To operate such an application with a network based location system, periodic location measurements would have to be performed, say at 10 minute intervals. Each of these location measurements requires the mobile to be activated, incurring a cost in terms of network resources and battery usage in the mobile. As an indicative cost, at the current time, mobile operators appear to be charging a similar rate per request to that charged for Short Message Service (SMS). In the example at hand, the location requests might continue for an extended period of days or even weeks without the customer being located near the store. The result is a very large accumulated cost for the locations without the store owner having the opportunity to send a single advertisement. Store owners and other similar potential users of such a system will not use services under such terms.
Hybrid Location Systems
In the most common hybrid architectures, measurements are made by the handset and then provided to a network based entity for position calculation. The limitation in this case is the same as for network based systems. Each position evaluation requires the transfer of measurements from the handset to the network based entity. This transfer could be via SMS, General Packet Radio Service (GPRS) or other wireless bearer however all incur a finite cost which accumulates with each cycle and in no fixed proportion to the commercial benefit being derived.
Handset Based Solutions
The limitations described in the previous paragraphs can be overcome using a system in which the location of the user can be monitored without a transaction cost. In the application example above, a cost should only accrue when the customer is in the vicinity of the store. Handset based systems can provide such a solution.
There are existing handset based solutions. Perhaps the most well known is the satellite based solution in which a Global Positioning System (GPS) receiver is integrated with the handset. This type of system can provide accurate, cost free monitoring of position and a transaction only when useful. One disadvantage of this solution is the relative low penetration of GPS enabled handsets in the marketplace This means that location based services using such handsets can be offered to only a small percentage of mobile subscribers. Further, reliable operation of GPS receivers is generally limited to outdoor environments with a reasonable view of the sky.
Another existing handset based solution provides a coarse Cell Identity (CID) based position calculation. This uses the location of the base station currently serving the mobile. The mobile knows the identity of the serving base station. If the mobile has available a table of base station identifiers and corresponding locations then an approximate location can be calculated. While this approach avoids the repeated location transaction cost, it suffers from a major disadvantage due to the inaccuracy of the locations. In some cases the errors can be several kilometers. Whilst techniques are known for obtaining improved accuracy using more sophisticated algorithms, these are unsuitable for implementation either on a handset or more particularly on a Subscriber Identity Module (SIM) card due to the very limited processing and memory resources.